When she visited the isles for the first time in 1975, it was for a summer job after she dropped out of university.

And when she decided to set one of her books there in 2005, it was to be a stand-alone novel.

But, like all the best crime fiction, there were twist and turns to come and the 58-year-old writer has enjoyed a special relationship with the most northerly outpost of the UK for almost 40 years.

Ann visits three or four times a year and met her husband Tim there.

Her first Shetland novel Raven Black won the inaugural Duncan Lawrie Dagger Award from the Crime Writers’ Association. It was the start of a quartet which comprises White Nights, Red Bones and Blue Lightning.

Her latest book, Dead Water, is the first of the next four to be set on the outlying chain of more than 100 islands, 120 miles off the north coast of Scotland.

It precedes a major new BBC adaptation starring Douglas Henshall as her detective Jimmy Perez which will bring her books and Shetland itself to a new audience.

Ann, who is originally from Devon but now lives in Whitley Bay, Northumberland, said: “I have a love affair with Shetland and it has been going a long time.

“I first came when I dropped out of university and had a chance meeting in the pub with someone who was going up to become an assistant warden in a bird observatory and who wasn’t sure he had made the right decision.

“I said, ‘It sounds great.’ He phoned up a fortnight later and said they were desperate for an assistant cook. So off I went, not knowing exactly where it was. I thought vaguely it might be one of the Western Isles.

“I loved it. I met my husband there, who came as a visiting ornithologist to the bird observatory on Fair Isle the following year, and I’ve been going back ever since.”

Her love of Shetland and the islanders meant Ann was reticent about setting a book there.

When she did, she had no idea that it would lead to such a successful series – and neither did her publishers.

Ann, who has two daughters and six grandchildren, said: “I know when the idea for the first book came because a very rare bird turned up in Shetland between Christmas and New Year and my present to my husband was a day trip to see it.

“It had snowed, which isn’t that common in Shetland, and had frozen over. It was one of those really clear, stunningly beautiful days and we saw three ravens, very black against the snow.

“Being a crime writer, I thought, ‘What if there was blood there as well?’ The colours were like something from a fairy story and I started off with that.

“I thought it would be an impertinence to set a novel there because, although I know it very well, I don’t live there.

“I was thinking it would be a short story but then I went back six weeks later and got chatting to the arts officer and he said, ‘Just go for it – we could really do with a mainstream novel set in Shetland.’

“He put me in touch with a local ex-policeman and I gathered all sorts of small details such as the fact that, if a murder took place, the Serious Crime Squad would come in from Inverness so it wouldn’t be local police who deal with it.

“It just got me thinking about what it would feel like if you spent your whole career dealing with driving offences or brawls in bars and then you get a murder and you can’t deal with it.

“The funny thing is that, when I wrote Raven Black, I showed the first few chapters to my editor.

She said, ‘I really love it but you do understand that it has to be a one-off – you will be stretching credibility too far to have more than one book with a load of murders in Shetland.

“Then it won the Dagger, got well reviewed and suddenly it was, ‘Okay, we could do a short series.’

“I love going and can’t imagine not writing about Shetland now.”

Ann is sensitive to islanders’ feelings in her books and gets a Shetlander to read her work before it goes to a publisher. She also makes sure she does a book launch, library events and school workshops there when a book is published.

She said: “People have always been very supportive and helpful.

“I think, in a way, it helps that I’m a real outsider. I’m a visitor and understand I am never going to know what it’s like to be a Shetlander.

“The first book has a character called Robert Isbister and somebody once came up to me and said, ‘I could never write a book with a character called Robert Isbister in it because I know seven Robert Isbisters and they would all have thought I was writing about them.’”

New TV drama Shetland has been adapted from the third book in the series, Red Bones, and is based around the murder of an elderly woman who crofts the land where an archaeological dig is taking place.

It climaxes with Shetland’s famous Viking fire festival Up Helly Aa.

Ann is grateful but not surprised that the islanders literally pushed the boat out to help recreate the spectacle for the cameras.

She said: “They had to close the streets in the middle of the night because they were filming in June and it doesn’t get dark until about 11pm.

“The festival committee dressed up, grew their facial hair, dragged a galley through the streets and everybody came out.

“There are very few places where you get that sort of support and I haven’t heard anyone moan about the inconvenience.”

A screening has already been held on the island and was received enthusiastically, much to Ann’s relief.

She said: “The BBC were aware of the help they had from Shetland and did a preview screening in November.

“I was so nervous but it went really well and they were caught up in the drama.”

* Dead Water is published in the UK by Pan Macmillan and is out now. Shetland is due to be screened by the BBC in March.